Assigbiob to general electbic



M. UN,GER.

'INDUCTION FURNACE- APPLICATION FILED APR-'21. I919.

' Patented Dec. 23,1919.

2 swans-sun? I.

Inventor. Magnus Linger, b 4. M

His fltLorneg.

, UNGER." moucnou FURNACE.

APPLICATION FILED APR.21. 1919.

71,326,120. Patented Dec. 23,1919.

2 SHEETS-SHEET 2- inventor 'Magnus Llnger,

MAG-NUS UN GER, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

To all whom it-mdy concern:

Be it known that I, MAGNUs UNGER, a citb zen of the United States,residing at Pittsfield, in the county of Berkshire, State of operation.It is possible that certain limita-' tions which were believed to beinherent in such a construction have interfered with the practical useof this structure, as for example, the belief that it is necessary tolocate the legs of the core outside theessential parts of the leakagefield ofthe primary winding and the charge constituting the secondary.Such a construction would necessitate a larger core with correspondingincrease in cost, core loss and exciting cur rent. I have found that thereduction in stray flux would be negligible.

I have discovered that it makes no appreciable difference in the powerfactor of the furnace to place the legs of the core closely to theprimary winding and the charge container.

It is the object of'my invention to provide an induction furnace havinga primary winding located above the charge container and embodying theabove and other improvements hereinafter pointed out with particularityin the appended claims.

A complete understanding of my invention may behad from the followingdescription taken in connection with the accompanying drawings. Figure 1is a top view; Fig. 2 1s a vertical section of a furnace embodying myinvention; Figs. 3 and 4 illustrate structural details; and Fig. 5,Figs. 6,

6 and Figs. 7, 7 illustrate arrangements and electrical connection ofthe primary wi i g,

Specification of Letters Patent.

about 60 to- 90;

INDUCTIONFURN ACE.

Patented Dec. 2a, 1919.

Application filed April 21, 1919. Serial No. 291,615.

Referring to the dra-Wingand particularly to Fig. 2, the furnacecomprises a magnetic core consisting of vertical legs .1, 2., 3, a

horizontal lower yoke 4 and a horizontal upper yoke 5 connecting thevertical legs 1, 2 and 3. The primary winding comprises a flat coil 6consisting in some cases of several interconnected sections, ashereinafter described in connection with Figs. 5, 6 and 7. The terminals7, 7 of the primary winding'are shown in Fig. 1.

. The charge to be treated is contained within an annular crucible 8located beneath the primaryiwinding 6 and surrounding the central leg 2of the core. The crucible 8' is provided with an' outer shell 9 ofsteel, or other suitable metal, which has one or more insulated jointsto break the electric circuit. It is lined with a layer of fire brick10, inside of which is'an inner lining 11, consisting of highlyrefractory material, as, for example, crystallized magnesia, preferably,n'iagnesia which has been molten, allowed to crystallize and thereuponpowdered and rammed into place with a suitable: binder.

As shown in Fig. 20f the drawing, the sidewalls of the crucible areoutwardly inclinedso as to make an-an'glewith respect to each other ofabout 60 to 90,that is, lines passing through. the intersection of aver- 'tical plane with the opposite side walls meeting. at an anglewithin the l imits o'f This construction has the following advantages;It provides a shallow furnace chamber in which a given amount of charge,such as melted steel, can be brought closer to the primary winding 6than ina deep narrow furnace chamber; (2) the position of the wallsenables them to be easily repairedwhen cracked or worn out'by the actionof the charge and the slag; the meniscus of the melted charge is morenearly flat and hence there is less slag required to completely coverthe melted metal than in a deep narrow chamber in which the meniscus isdriven down on one sideand up on the opposite side by the magneticaction of the stray flux to a greater degree than in a'shallow chamber;(4) the heating action of the current induced in the charge is greatestat the surface, that is,nearest the primary: winding. Hence in awlde,shalof the core being first removed.

The crucible is provided with a cover 1:5 I

of silica lire brick, crystallized niagi'iesia, or other suitablerefractory material. l he cover 12 is preferably prorided with rings 13,ll, of iron or the lil e, on its inner and outer side. walls, and theserings may be provided with bands 1' to which hooks may be appliedcciivcnience of removal of the cover if as indicated at 17.

The primary winding (3 is provided with a CtlSllli? or housing 20,consisting of noin magnetic ni-rtcrial, such for example, as brass, or25)? nickel steel. The central leg; 2 of the core is provided withcasino; ll. spaced away from the core and providin e space for thepassage of the cooling: fluid,

The lowerL finally emerging thr ugh outlet openin at the pcriph of thecasino ".20.

ably openings are provided for the passage of some oi: the cooling airover the top of the cover 12. I

Circular angle irons it) and :3? rest upon the yoke .5. and act supportsfor the pri mary coil ti and Sll1ll ll11(llll2f casing which areconnected thereto by studs 2b. lheforably. the cover 12 is alsoconnected to one of the angle iron supports, for exam-- pic, byconnecting; rods already referred to. This construction enables theyoke, primary coil, its casing and the cover of the furnace to beremoved as a unit. the bolts to connecting' the yoke to the vertical lcin this manner convenient access may be had to the charge within thecrucible. which is then entirely exposed.

The entire furnace is supported within a frame 31. hungby the shaft 32on trunnions 33, so as to cnablelhe furnace to be tilled by anyconvenient means. such as the hand wheel ill. for the removal of thecharge.

As shown in Fig. 1, a number of charging doors 35. 36. and 37 maybeprovided for the introduction of metal to be melted. slag formingmaterials and the like. Convenient, access is provided thereby to allparts of the such as air. end of the 21 connects with an inlet tube theupper end reg as with an inlet o into the casing 20. A. blast of air relthrough the inlet tube 2;. passes .oin l the core 12 and from thencearound the ci charge in the crucible, rendering convern lent thesupervision of slagging operations and the like. A pouring spout 38provided for the discharge of the metal. and slag.

Cihe magnetic core of the furnace is so proportioned and designed thatthe mag; nctic flux density will be substantially uniform when thefurnace is under load. The limiting feature determining the size of thecore of an induction furnace is generally not the core loss which isrelatively low on accountof the low frequencies used. On the other hand.the factor which is of considerable importance is the exciting currentrequired for the primary windings. The greater-the exciting; current thelower will be the power factor at which the furnace will.

operate. By proportioning the core to give a substantially uniform fluxdensity at load current. there will be a substantial reduction .in thecore loss as well as in the exciting current render load conditions. Thelower yoke l; of the core because of its more remote location from the.primary and secondary winding' has a lower flux density than the upperyoke This is not only in accord with theoretical considerations takinginto account the leakage iclds but has been {13(- ariincntallydetermined by me.

in order to operate the furnace substantially uniform flux densitylargest cross-sect on to the top 'hc same flux with a.

yoke I) is illla will have nearly density as at. no load. The vciucallo 1. 2 and 3 bottom \'()l\'@ 4- will have cross-section 503% less thanthe. cross section of the top yoke. The actual proporticni of thesections will depend upon the particular design and is based upon thedistribution of the stray tin ln this manner the weight of the core maybe reduced .without sacrifice of ciliciency. For example, in a ill-toninduction furnace a core designed to give a uniform 't'iulv density ofno load. would weigh forty tons. The weight of such a core in a furnaceof the design illustrated herewith could be reduced about 15')? or morein weight of material with a correspoiulingly reduced cost.

There is always some danger in an induction furnace of a fracture of thelining and the escape. of molten metal through the break with consequentoamac'c to the core and other parts of the furnace. As already indicatedabove. I have provided a shield about the core to obviate damage by theescape of molten metal.

Figs. 3 and -l illustrate in section specific forms of shieldsen'ibodying my improvement. The shield illustrated comprises a metalform i1 upon which are located a layer 42 of refractory fire-proofmaterial such, for example, as mica, and an; outer I gri vo I 21 5culatoiji current"being set-up in the bath 111 some sizes of furnaces alayer of asbestos aprlmary winding, upon sald core and a layer 43 offibrous refractory material, such as'asbestos. As asbestos fabric losespart of its mechanical strength at a temperature ofabout 200 to'300 C.due to a burn-out of the cotton binder commonly used, I prefer toimpregnate the asbestos with'a binder, such as a phenolic condensationproduct. The heat insulating properties of asbestos and mica serve asadequate protection even for molten steel at 1600 C. In some cases themetal backing may be omitted and in fact alone will furnish adequateprotection.

Although in Fig. 2 the primary winding of the furnace has been indicatedasconsisting of two sections, it is desirable in some cases .to providemore than two sect1ons. In any event, whether two sectlons or agreaternumber are used I provide 0on v,magnetlccore, a primary wmding thereons5 nections and switching means for supplying one of these sections or acombination of sections with current to the e zclusion of the; I othersections in order to ad uStthe shape of the meniscus of the moltencharge in the furnace'brucible. For example, in Fig. 5

-I have shown a primary coil consisting of I sections 45$) 4'8provided'with separate conductors 49 'to..53', and respective switches"54:

to 58. By closingswitches 5,4.and 55 current can be sent throughsection. while the remainingxsections remain open-cir- -cuited, and inthe same way by closing switches '54: and .56 while the remainingswitches remain. open current may be sent through the sections 4E5and 46in series. In

this-'maiiner the magnetic center of they excitation may be shifted fromthe inner toward the outer periphery of thefurnace crucible. The effectof this is'illustrated more clearly in Figs. 6 and 6 and? and 7 In Fig.5two groups of coils 59 to 62 and 63 .to' 66. are connected electricallyin parallel 2 through the conductors GZand 68. In that case} wtheemoltencharge; assumes a shape somewhat-as shown in Fig. 6, a single cirasindicated by arrows. This single cir- L I culatory efi'ect lasjdistinguished from the double circulation is. distinctive-ofa fur-' nacebuilt in accordance with-my invention having a shallow cruciblewith-{diverging walls A single circulation as illustrated obviate thedeleterious suction effect on the allrcaused by a'double circulation.

69. 'This UQQYQIQIiQSS- iIi thG shape-of the meniscus requires a largeramount of slag to fully cover. jfthe m'etal at-the High point of'thebath than wouldberequired with a more level-meniscus. .It is preferable;

therefore for some-metallurgical o 'erations to change' the connectionsby shi ing-the switches 71, 72, 73, 74' and 75 to conne ct',the

coils 59, 60, 63' and 64 in series, asiiiidicated shape of a; meniscus.shown in ere '1s.a;.depress1on at th'e'po'int I in- Fig. 7. 70

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is 1. An induction furnace having a melting chamber, the sidewalls of which are outwardly inclined and makean angle of about 75 '60towith respect to each other.

2; An induction furnace comprising acore,

furnace chamber located below said primary Winding and adapted tocontain a charge, the 0 -Walls of said chamber being outwardlyinclinedabout 60 to 90 with respect to each other.

3. An lnductlo'n furnace comprlsing a and a crucible located beneathsaid winding for containing a charge constituting a secondary winding,the legs of said core being placed closely about said primary andsecondary windings within the leakage fields of 90 said windings. I 4.An lnductlon furnace comprislng a core I having a removable yoke, aprimary winding upon said core, a charge-containing chamber located uponsaid core, a cover therefor, '-means mechanlcally connectlng togethersaid yoke, cover and all parts above said chamber -1I1 order toenablethe same to be removed'as a unit in the operation of said furnace toexpose a charge within said crucible. 1 5. An inductipn furnacecomprisinga core, 'a primary winding interlinked .magneti cally Withsaid core, a housing for said winding, a removable yoke for saidcore,.means for mechanically connecting said yoke, winding and housing,and a .charge "containing chamber located beneathsaid primary wind- .6.An inductionfurnacecomprising acore, a remova ble yoke for said core, aprimary wlnd no" interlinked ina'gnetically with said core, a ousing'forsaid winding, havin in- .let and outlet openings, means" attac ing saidwlndlng, and houslng to said yoke and a housing'for said core providingspace for a "cooling fluid and communicating with the inletof thehousing for the primary coil. 7{' jAn:1nduction furnace comprising acore 'having a' disengageableyoke, a. primary winding for, said core, acrucible for contaminga charge constltuting a secondary windingnafcover'for said crucible and means connecting said yoke, primary winding andcover to enablethe same to be removed as 8 Aninduction furnacecomprising a core,

a charge container surrounding-said core,

a primary-Winding consistingv of a plurality ofsections located uponsaid core abovesaid 13o container, and switching means for varying theelectrical connection of said coils to each other. v

9. An induction furnace comprising a core, a refractory containeradapted to contain the charge constituting the secondary" winding of thefurnace and a primarv \Yindino' for said furnace consisting of aplurality of sections, and switching means exciting one or more of saidsections to the exclusion of other sections in order to vary therelation of the magnetic center of said primary Winding to the furnacecharge.

10. An induction furnace comprising a primary winding thereon, acrucible adapted to contain the charge constituting the secondaryWinding, a core of magnetic material linking said windings, said corebeing located in part beneath said crucible thereby subject to contactwith the accidental escape of molten material through a fracture in saidcrucible, and a shield located between said crucible and parts of saidcore exposed to crucible adapted to contain a charge constituting asecondary winding, the cross-section of said core being proportioned togive substantially uniform flux density when said furnace is operated atload.

In witness whereof I have hereunto set my hand tliis'lSth day of April,1919.

' MAGNUS UNGER.

